Publisher's Synopsis
Excerpt from The Ceara Rubber Tree in Hawaii
The latex, or milky sap, of the rubber tree is of very complex composition, containing starch, sugars, gums, resins, proteids, and salts, as well as rubber. The milk tubes are not continuous - that is, it is not possible by cutting through the network of tubes at the base of the tree to drain out all of the latex. The latex-bearing tissues may rather be compared to a series of short tubes joined end to end with permeable diaphragms between. In the living plant there is free transfer of latex from one tube to another, but there is no circulation comparable with the circulation of the blood in ani mals. There is no rise and fall of the sap, as is the common belief, and so far as has been determined, there is no ruling direction of movement at any time of the day or period during the growth of the plant. The circulation of the sap in the tree or of latex in the milk tubes is simply a process of life, a phenomenon of growth.
The rubber in the latex in the milk tubes is supposed to exist as an emulsion, somewhat comparable to fat globules in milk. When a milk tube is ruptured, to permit its contents to escape, the rubber globules rapidly agglutinate, the function of rubber apparently being to close up wounds and prevent the loss of water from the tree by evaporation.
The flow of latex when the milk tube is ruptured is not due to the continuity of the tubes, as would be supposed, but is because the latex is under tension in the growing trees. When the pressure is relieved by the breaking or cutting through of the tissues containing the latex, the tension being released, the milk tubes for a short radius around the wounds quickly empty themselves of their contents.
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